Signal-seeking tuner



W. L. DUNN SIGNAL-SEEKING TUNER Filed NOV. 5, 1945 INVENTOR. WlLilM Lv DUNN M/haw ATTORNEYS Mamh 7, 1195@ A UK Patented Mar. 7, 1950 2,499,573

UNITED STATES PATENT OFFICEv 2,499,573 SIGNAL-SEEKING TUNER William L. Dunn, Glenview, Ill., assignor to Belmont' Radio Corporation, a corporation of Illinois Application November 5, 1945, Serial No. 626,679

8' Claims, (Cl. 250-40) 2 This invention relates to signal-seeking tuners is a detailed view of the driving connection. from and more particularly tosuch tuners for radio the driving motor to the tuning apparatus. 1 'roadcast receivers of the type which sweeps over Referring now to Fig. 1 of the drawing; there the tuning rangeuntil a station is reached from is represented a complete radio-broadcast receiver which the signal is above a predetermined miniincluding an automatic signal seeking: tuner em mum acceptable signal strength, and which rests bodying the invention. This receiver comprises in such positio a radio-frequency amplifier unit l having input In certain broadcast receivers it isdesirable to terminals connected to anantenna-ground'circuit procure the easeof tuning characteristic of push- II an u p terminals connected t0 n Oscillab'utton tuning apparatus while at-the same time 10 tor-modulator unit I2. This latter unit is in turn it is desired to avoid the presetting feature charconnected to an intermediate-frequency amplifier acteristic of such tuners. For example, in the I3, a frequency discriminator described in cas f au omobile receivers the tuning of the more detail hereinafter, a. portion of whichserves local stations of greatest signal strength varies a so s a od detection The, d t d from place to place'so that it becomes impracti- 15 modulation signal is app by ye a Circuit cableto set up a push-button tuner in such a Way I5 and a coupling condenser I6. to a volume: conas to be useful as a car is driven over considerable rol r sistor I I havin an adjustable contact IIa distances which in turn is connected through an audioprovide a new and improved tuner for a adi as aloud speaker I9. An automatic amplification of conventional push-button tuners but does not suit 5 and applied, as indicated, to on or more require any presetting operation of the vacuum tubes of the units It, I2v and I3: to

It is another object of'the'invention to provide maintain the amplitude f the Signal nput o a new and improved tuner for radio broadca t the frequency discriminator I4 approximately receivers of the signal-seeking type; that is, a constant for wide range received signal intensituner in which one operation of a push-button tiese radio-frequency amplifier D d d will cause the tuner to seek a signal of acceptable w th nput and tp tuning units schematically field strength and to hold on to such st ti until represented at Ito and Ilib, respectively; while the he push-button is operated a second time wh w oscillator-modulator unit is provided with an: ad-

the cycle is repeated. justable tuning unit 12a.

In accord'ancewith the invention, an automatic The adio r ceiv r d sc ibed, per se, forms no signal-seeking tuner for aradio receiver compa Of t pre ent nven o d o s in prises an adjustable tuning apparatus for the reaccordance with conventional pr n 80 that paratus, manually operable means for initiating unnec sary. In bri f, how v r, nals in rope ation of the power means, and means respgncepted by the antenna system I I are selected and sive to the reception of'a signal by the receiver amplified in the unit I0, converted in the unit for arresting the actuation of the tuning appa I2 into intermediate frequency signals, further ratus'. Preferably the tuner includes also an in- 40 selected and amplified in the unit I3, and detected terlocking means interconnecting the manually in the unit It to derive the modulation signal. operable means and the signal-responsive means This signal is impressed upon the audio-frefor limiting the latter to a single operation after quency amplifier I8 wherein it is further. amplieach. operation of the manually operable means. lied and applied to the loud speaker I9 for re- Fora better understanding or the invention toproduction. The AVC connection from the unit gether with other and further obje'ctsthereof', refit serves to maintain the average signal input to erenceis had to the following specifications taken the u it [4 approximately onstant and thereby 1n conJunction with the drawings, while its scope avoids overload of the receiver for strong signals,

will be pointed out in the appended claims. while providing maximum amplification for weak Referring now to the drawing, Fig; 1 is a circuit signals.

diagram, partially schematic, of a complete si'g- The automatic signal-seeking tuner of the innal-seeking tuner for a radio hroadcast're'ceiver vention is shown schematically n d: in

and embodying the invention," Fig. 2 is: a schemoredetail inFig. 2. IngeneraLthis tuner commatic representation of the physical constructio prises jus fi apparatus t eof the-signal seeking timer of Fig; 1'; while Fig. 3 ceiverindicated schematically-as the tuning.

unit 26 supporting the shaft 24 1 sleeve 321.

Illa and Nb included in a radio-frequency amplituning unit 12a in the oscillator- While the tuning apparatus may be of any desired type, there is illustrated by Way of example tuning units comprising an adjustable-permeability inductor in parallel with a fixed capacitor. As shown in Fig. 2 the inductors for the tuning units Illa, lob and 12a are represented at 20, 2|, and 22, respectively, provided with adjustable ferro-magnetic cores 20a, 2la and 22a, respectively, supported from a common reciprocating yoke 23. The yoke 23 is securely mounted on an elongated operating shaft 24 longitudinally adjustable in bearings or housings 25 and 26. This tuning apparatus includes also means for biasing it to one extreme position, for example, a tension spring shaft 24 by way of a an idler pulley 29.

The tuning apparatus also includes power means, such as an electric motor 30 energized from suitable source +A, which may cathode heater supply for the receiver, for actuating said tuning apparatus against the biasing spring 21 in only a single direction from one of its extreme positions. The motor 30 is energized from source +A through a control circuit to be described and represented schematically in Fig. 2. The motor 30 may be connected to drive the shaft 24 in any suitable manner, for example, by way of an inching drive shown in more detail in Fig. 3. Essentially this comprises an eccentric 39a mounted on the end of the shaft 30b of the motor and engaging a sotted collar 3| surrounding and movable axially of the shaft 24. The inner surface of the collar 3| is conically tapered, as shown, and forms with the shaft 24 an annular recess. Within this recess is mounted an axially movable e ongated annular sleeve 32 having a flexible line 28 passing over plurality of peripheral apertures 32a in which are mounted ball bearings 33. One end of the sleeve 32 is provided with a radially outwardly extending flange 32b which is engaged by a compression spring 34 acting against the housing 25 to bias the sleeve 32 to the left as shown in Figs. 2 and 3 and thus wedge the ball bearings between the collar 31 and the shaft 24 to provide a frictional driving engagement therebetween.

The tuning apparatus of the invention includes also manually operable means for initiating operation of the power means, which may be in the form of a manually operable push-button switch 35 having normally open contacts 35a and 35b in circuit with the motor 30 and auxiliary normally closed contacts 350 and 35d. The apparatus also includes brake means for restraining the tuning apparatus from movement under the influence of the biasing spring 21. The driving unit 25 described above in itself constitutes a brake means when the motor 30 is de-energized by virtue of the biasing of the sleeve 32 to a braking position by means of the spring 34. The

comprises additional braking means which may be identical to that of unit 25 except that there is no provision for reciprocating the collar 3| to actuate the drive shaft 24. The unit 26 also includes a biasing spring 341 acting on the flange 32121 of the brake The receiver also includes means for normally quieting the receiver except when it is tuned to a desired station of acceptable signal strength. This may comprise a connection l8a to audio-frequency amplifier 18 by way of a circuit 36' adapted to be grounded by a control means 'toibe .described and thus mute the amplifier 18,.

The signal-seeking tuner further includes control means responsive to the reception of a signal of a predetermined value by the receiver, only upon tuning through the signal, for arresting the actuation of the tuning apparatus, as by setting the brake means, and for rendering the quieting means ineffective. This control means comprises the frequency-responsive discriminator network l4 described above, connected to translate a received signal and effective to develop a control signal. The discriminator l4 comprises a primary tuned circuit Ma coupled to a secondary tuned circut I41) and a tertiary tuned circuit also coupled to the primary circuit 14a and provided with an electrical midpoint 14d to which is applied a signal from the secondary circuit 14b. The sum and difference of the secondary and tertiary signals are rectified by discriminator diodes Me and 14) connected across the tertiary winding 14c and provided with individual load resistors I49 and 14h. The detected moduation signal is derived from the resistor Mn and impressed upon the volume control resistor l1, as described above. The control signal or output signal of the discriminator i4 is derived at the terminal I41 and applied through grid resistors 31 and 38 to the control grid of a control-signal amplifier tube 39. As is well understood, the control signal developed at the terminal Mi of the discriminator l4 has the usual S-characteristic which reverses polarity as the receiver is tuned through the center of the channel of the station being received. Since the actuating means for the tuning apparatus operates in only a single direction, it is desirable that this actuation should not be interrupted until the tuning apparatus is adjusted to the center of the channel; that is, it is desired that the portion of the control signal developed while tuning toward the center of the channel be made ineffective. To this end, there is provided means for suppressing the portion of the control signal developed while tuning toward a received signal whereby there is developed a control signal only during tuning through and away from a received signal. This means comprises a connection from the junction of resistors 31 and 38 to an auxiliary diode anode 39a of tube 39.

The control means of the tuning apparatus also includes means for utilizing the control signal developed as described. This means may comprise an electromagnetic relay 4i having a winding 4Ia controlled or energized jointly in response to the control signal developed by discriminator l4 and the manually operable switch 35. Specifically, the winding 41a is energized from a suitable source +B through a load resistor 40 and the vacuum tube 39. The relay M includes a movable contact element 4lb biased by a spring 4| 1 to form with a stationary contact 41c normally open hold-in contacts in parallel with the contacts 35a, 35b of the switch 95, to form with a stationary contact 4le, normally open muting contacts controlling the muting circuit 36; and to form with a stationary contact 11 normally closed interlocking contacts in series with the normally closed contacts 35c, 35d of the switch 35. In parallel with the winding 41a of the relay and the tube 39. is a resistor 42 having an adjustable contact -42a connected-to ground and comprising means for adjusting the electrical responsive means, that is the relay 4| to respond to received signals of different predetermined .values.

T nt -means l na e kms t n also includes interlocking means: interconnecting the manually operable switch 135' and the. signal v:responsive relay 4| 'tacts 35c, 35d of switch- :35, and normally closed contacts 41b, d of the. relay '41, thus reducing the energization of therelay below an-operating value.

The tuner further includes meansresponsive to adjustment of the tuning apparatus to its other extreme position, treme of its range of adjustment 'by the motor 3!) against the biasing spring 21, for initiating return thereof to its initial extreme position under the influence: of

indicating scale or with the drum 5H0! cooperation with a circu ar indicating scale. The-drum 50 is provided with an annular 'frictional'driving The tuning are normally biased by means ota'sprmg 53' :so

contact 48a in the circuit of thebrake magnets 4'5 and 4'6 and comprising means actuated by the engagement 'of' the manual tuning element with the drum '50 for energizing the brake magnets to re'lease the'brakes and free the tuning apparatus from actuation by the driving motor '30 and from restraint by the brakes 25 and '26.

In considering the operation of the: signalthat init ally "the several control switches are. the positions illustrated in thetdraming that thereceiver isnotztunedztoa 'StEtriUlIiUiflECEE-QtflblE eas -the.

ill

axially adjustable and 1 -;ingtheou1eting ormuting bias :hrake. magnets and :46 are lie-energized, :the interlocking circuit 43. of the relay winding is closed through the contacts 350, 35dand4lb, 41d 4.! is unresponsive to control signals from the discriminator .l4 while "the enof the motor 39 is open :at the 35b and 4th,, Me in vparallel. If new the automatic push-button switch 35 is Mb, Me and Mb, Me. Thus the relay 4| completes the holding-circuit for the motors!) so that the. push-button 35 need be depressed only momentarily'.

gagement between the collar 3| and the shaft 24, inched to the right against the action of the biasing spring Win a series of rapid, minute, step-by-step movements. Movement of collar 31 to the left by the eccentric 30a releases of the biasing spring '21.

As the receiver is tuned into a channel which'is pressed or 'short-circuited 'by the auxiliary diode 39a 'so that no appreciable control "signal is aprapidly negatively acteris'tic of the discriminator alongthe conventional S-ch'ar- 14 so that, when to the center of the channel of thestation being received.

Simultaneously the contacts 41h, 4.1a are opened, thus opening the circuit 36 connected to 'the terminal- [8a of the amplifier I8 and removtherefrom. ,Simul are closed again, cuit 43 through the contacts 350,

'the energization of the relay winding receiver in case 'further prevents receiver in case it should be turned off and then 'tion, as shown in 'ated to open driving 50a, whereupon the drum 50 can that, in releasing the tuning the tuning apparatus is radio receiver comprising apparatus for the receiver, power means for actuimeans, means responsive to interlocking cir- 35d of the switch 35, contacts 4|b, 41d of relay 4| and resistor 44 to the high-potential terminal of the relay winding 4la. This connection is effective to reduce Ma to such a point that it will not respond upon the removal of the control bias from the tube 39, in case the signal from the received station should be interrupted for any reason. This interlocking arrangement avoids disturbing the setting of the the station being received should interrupt its broadcasting only momentarily and an automatic retun ng of the completing the was being reconditions, it is necessary to depress the automatic tuning switch 35 again to initiate the cycle described above.

In case the described above, to its extreme right-hand posithe drawing, without receiving any signal of acceptable strength, the limit switch 48 is actuated as by the yoke 23 to close its contact 48a and thus energize the brake magnets 45 and 46 which are effective to move the sleeves 32 and 321, respectively, to their right-hand positions and hold them in these positions, thus releasi'ng both of the brakes 25 and 26. The spring 21 then acts through the line 28 to operate the shaft 24 and the associated tuning apparatus to its extreme lefthand position, as shown in the drawing, representing the high-frequency limit of the tuning range. The limit switch 48 remains closed until the tuning apparatus reaches its other extreme position, whereupon it is operthe contact 48a and de-energize the brake magnets 45 and 46 and the brakes are reset by their respective springs 34 and 341.

In case it is desired to tune the receiver manually, the tuning knob 52 is depressed until the element 52b engages the driven element be driven to actuate the tuning apparatus through the endless belt 49, the clamp 24a and the shaft 24 in a conventional manner. Upon the depression of the tuning knob 52, the switch contacts 55 are closed, thus energizing the brake magnets 45 and 46 to release the brakes 25 and 26, respectively, to permit the justed by the tuning knob 52. It will be apparent knob 52 after a tunthe switch contacts 55 must be opened before element 521) disengages the driven element to ensure that the brakes are reset before the manual driving connection to interrupted.

Thus it is seen that by the invention there is provided a signal-seeking tuner which has the ease of tun ng characteristic of conventional push-button tuning apparatus but requ res no presetting of one or more manual push buttons.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes and modiing operation,

'fications may be made therein without departing from the spirit or scope of the invention.

What is claimed as new is: 1. An automatic signal-seeking tuner for a an adjustable tuning ating said tuning apparatus, manually operable means for initiating operation of said power the reception: of-:a

tuning apparatus should operate, as

tuning apparatus to be freely adating said -motor means, electrical normally open radio receiver comprising, apparatus forthe receiver, r for actuating said tuning apparatus, a manually operable switch including motor controlrcontacts signal by-the receiver for arresting the actuation of-said tuning apparatus, and interlocking means interconnecting said manually operable means and said signal-responsive means for rendering the latter non-responsive after a single operation until a subsequent operation of said manually operable means.

3. An automatic signal-seeking tuner for a radio receiver comprising, an adjustable tuning apparatus for the receiver, power means for actutuning apparatus, manually operable means means, means responsive to the reception of a signal by the receiver for arresting the actuation of said tuning apparatus, manually operable means engageable with said tuning apparatus for adjusting the same, and means actuated by engagement therebetween for freeing said tuning apparatus from actuation by said power means.

4. An automatic signal-seeking tuner for a radio receiver comprising, an adjustable tuning apparatus for the receiver, power means for actuating said tuning apparatus in only a single direction, manually operable means for initiating operation of said power means, a frequency discriminator network connected to translate a received signal for developing a control signal, means for suppressing the portion of said control signal developed during tuning toward a received signal, and means for utilizing said control signal for arresting the actuation of said tuning apparatus.

5. An automatic signal-seeking tuner for a radio receiver, comprising, an adjustable tuning apparatus for the receiver, electric motor means for actuating said tuning apparatus, a manually operable switch for initiating operation of said means responsive to the reception of a signal by the receiver for arrest- .ing the actuation of said tuning apparatus, and an switch and said electrical responsive means for interlocking circuit interconnecting said limiting the latter to a single operation for each operation of said switch.

6. An automatic signal-seeking tuner for a radio receiver comprising, an adjustable tuning apparatus for the receiver, electric motor means for actuating said tuning apparatus, a manually operable switch including normally open contacts in circuit with said motor means and auxiliary contacts, electrical means responsive to the reception of a signal by the receiver and including hold-in contacts in parallel with those of said switch, and an interlocking circuit interconnecting said auxiliary contacts of said switch and said electrical responsive means for limiting the latter to a single operation for each operation of said switch.

7. An automatic signal-seeking tuner for a an adjustable tuning electric motor means 10 in circuit with said motor means and auxiliary reducing the energization of said electrical renormally closed contacts, electrical means responsive means below an operating value, thereby sponsive to the reception of a signal by the reto limit the latter to a single operation for each ceiver and. including hold-in contacts in circuit operation of said switc with said switch motor control contacts and nor- 5 WILLIAM L. DUNN. mally closed interlock contacts, and an interlockmg circuit interconnecting said normally closed REFERENCES CITED contacts of said switch and said electrical re- The following references are of record in the sponsive means for limiting said electrical refile of this patent: sponsive means to a single operation for each 10 operation of said switch. UNITED STATES PATENTS 8. An automatic signal-seeking tuner for a Number Name Date radio receiver comprising, an adjust le unin 1,968,302 Maurer July 31, 1934 apparatus for the receiver, electric m r means 2,056,200 Lowell Oct. 6, 1936 for actuating said tuning apparatus, a manu y 15 2,099,719 Banning Nov. 23, 1937 operable switch for initiating oper tion of id 2,326,738 Andrews Aug. 17, 1943 motor means, electrical means responsiv to z 2,369,542 Dietrich Feb. 13, 1945 reception of a signal by the receiver for arres ing the actuation of said tuning apparatus, and FCREIGN PATENTS an interlocking circuit interconnecting said 30 Number Country Date switch and said electrical responsive means for 351,934 Great Britain June 19. 1931 

